Last month Google came out with some new synthesized voices for Google Translate, and now the Google Mobile Blog has announced the availability of an iOS version of Google Translate, complete with voice-to-text data entry and synthesized speech. There's support for 15 languages via voice entry, but you can listen to the translation of 23 languages via those synthesized voices. Tapping a zoom icon makes the translated text bigger, handy when you want to just point and ask "where is the bathroom?" in Greek (or dozens of other languages).
Of course, the web app has been around for a while, but you couldn't do the voice or speech actions. The dedicated app is free, and I've found Translate to be quite good at what it does.